New high performance polymers characterized by high strength, resistance to various types of radiation, superior electrical properties, minimal influence of exposure to hot/wet conditions on electrical properties, solubility in common organic solvents, high glass transition temperatures, low densities, low moisture absorption, high thermal and thermooxidative stability and optical transparency are needed as refractive films and coatings. Such materials will also be useful for high density microelectronics packaging applications including their use as interlevel planarizers and as low observable coatings, cable wraps, wire coatings, and thin film capacitors.
Current state-of-the-art, high performance polymers do not possess the combination of properties desired for many aerospace and electronics applications, among others. Polyimides, for example, because of their outstanding thermal stability, have been used as high performance films for a variety of the above-described applications. However, certain desirable combinations of the properties discussed above are not readily attainable with polyimides. The imide moiety, which is relatively polar, tends to absorb unacceptable quantities of moisture for certain applications. In addition polarizability of the imide moiety is likely responsible for the relatively high dielectric constants measured for most polyimides. While chemical modifications such as the incorporation of fluorine into polyimides simultaneously reduces their tendency to absorb moisture and their dielectric constants, other properties such as mechanical strength may be compromised. Moreover, even the incorporation of large quantities of fluorine into the polyamide structure does not reduce the influence of hot/wet conditions on key electrical properties to a desirable extent.
Incorporation of fluorine into other classes of polymers, for example into polyesters, has led to improvements in key properties such as thermal stability, solubility, and dielectric constant; however, as with polyimides, the fluorinated polyesters are not ideally suited for use in highly demanding electronics applications. Due to the polar nature of the ester moiety, these polymers exhibit relatively high dielectric constants and moisture absorption characteristics. Similar considerations apply when considering the incorporation of fluorine into polyamides, polycarbonates, and polybenzimidazoles.
Fluorine has also been incorporated into polybenzoxazoles. Unlike polyimides and other carbonyl-containing polymers, non-fluorinated polybenzoxazoles exhibit relatively low dielectric constants and moisture absorption. However, these polymers suffer from poor solubility in common organic solvents. Although the incorporation of fluorine increases the thermal stability and lowers both moisture absorption and the dielectric constant of these polymers, they still exhibit poor solubility in non-chlorinated, non-phenolic, (e.g, low toxicity), organic solvents suitable, for example, in microelectronics processing.
Therefore, new polymers which, when compared to polyimides and other high performance polymers, possess different combinations of the properties discussed above are needed.